Improve status bar height initial value

[mvasilak]

When the app state is restored to an open PDF document with a visible annotation toolbar, sometimes, due to the use of the extra UIWindow for the smoother instant presentation, there is not yet a foregroundActive connected scene, so statusBarHeight is set to 0, messing up the annotation toolbar placement.

You can reproduce this by:

• opening a PDF document
• show annotation toolbar
• kill the app
• launch app again (open document should be restored)

Fix moves the computation in viewDidLoad that allows an easier way to access the statusBarManager.

Also mentioned in this forum post